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Pisaster ochraceus - Ochre sea star

Geographic range:
Prince William Sound, Alaska to Isla Cedros, Baja California

Key features:
Largest 5-rayed intertidal sea star in the central coast of California. Can be purple, orange or brown, with thick rays and low, small white spines.

Similar species:
Pisaster giganteus -- Giant-spined star Pisaster brevispinus -- >Short-spined star Evasterias troschelii -- alse Ochre Star

Habitat(s):
bay (rocky shore), estuary, exposed rocky shore, kelp forest, protected rocky shore
Pisaster ochraceus - Ochre sea star image

 

Primary common name:
Ochre Sea Star
  ITIS code:
157253
Synonymous name(s):
--
General grouping:
Sea stars, urchins, cucumbers, sand dollars, brittle stars


Geographic Range
Range description:
Pisaster ochraceus can be found from the Prince William Sound, Alaska to Isla Cedros, Baja California.
Northern latitude extent:
--
  Southern latitude extent:
--
East longitude extent:
--
  West longitude extent:
--


Intertidal Height
Lowest intertidal height:
0 meters OR -2 feet
  Highest intertidal height:
0.90090090 meters OR 3 feet
Intertidal height notes:
Pisaster ochraceus can be found throughout the middle to low intertidal.


Subtidal Depth Range
Minimum depth:
0 meters OR 0 feet
  Maximum depth:
90 meters OR 299.7 feet
Subtidal depth notes:
Pisaster ochraceus can be found in the subtidal down to 90 m.


Habitats
Habitat(s):
bay (rocky shore), estuary, exposed rocky shore, kelp forest, protected rocky shore
Habitat notes:
Pisaster ochraceus occupies wave-washed rocky shores and pilings. Theses sea stars can live from well above the low-tide line down to about 90 m.


Abundance
Relative abundance:
Pisaster ochraceus is very abundant in the intertidal and is most common in the Northeastern Pacific since it is a cold water species.


Species Description
General description:
Pisaster ochraceus is among the most common sea stars of the rocky coast intertidal and occurs in great numbers on mussel beds. It is a member of the family Asteroidea in the class Stelleroidea, the sea star class. This sea star is amazingly adapted to the rugged intertidal habitats that expose it to severe stresses, including desiccation, big temperature changes, dilution by rainfall, and pounding waves. As part of its survival strategy, Pisaster ochraceus clings onto its substrate so strongly that many of its tube feet will tear off before the animal can be pulled from a rock. Fortunately, these tube feet regenerate and grow back quickly.
Distinctive features:
Pisaster ochraceus has a fairly large disk with 5 large, stout, tapering arms. May occasionally have as few as 4 arms or as many as 7. Its color is variable and can be yellow, orange, brown, reddish or purple. Tiny white spines form a network or pentagonal pattern on the central disk.
Size:
Pisaster ochraceus ranges from 15 to 36 cm in diameter.


Natural History
General natural history:
Pisaster ochraceus is considered a keystone species since it controls diversity and abundance of some invertebrates in the intertidal zone. Interestingly, many animals on which it preys can detect this star at a distance through its scent and escape. It is quite tolerant of air and is often exposed for up to 6 hours at low tide. This sea star has no protective camouflage, but it doesn't need this since it clings so tightly to rocks.

Adult Pisaster ochraceus grow in proportion to their food supply. Therefore, with abundant food, they grow faster, and if starved, they actually decrease in size. This makes their life span a debate, maybe 20 years or so. In addition to regenerating tube feet, Pisaster ochraceus can also regenerate arms that may have been lost.

Pisaster ochraceus has a very simple nervous system and lacks a brain. It simply has a nerve ring that encircles the mouth and connects with five radial nerves, which extend the length of the arms. They do have neurosensory cells scattered over their body that respond to mechanical, chemical and optical stimuli. However, sensory organs occur only at the base of each terminal tentacle where a great number of light-sensitive cells form an optic cushion which contains several ocelli, or simple eyes.
Predator(s):
Sea gulls, Laridae sp., and sea otters, Enhydra lutris, prey on Pisaster ochraceus. They also have microscopic predators as well, most notably infectious agents such as microbes.
Prey:
Pisaster ochraceus preys heavily on barnacles, such as the Leaf Barnacle, Pollicipes polymerus and mussels, such as the California Mussel Mytilus californianus. It may also eat Tegula snails, clams, limpets, chitons or anything else it can get its stomach onto.


Feeding behavior
Feeding behavior(s):
Carnivore, Omnivore, Scavenger
Feeding behavior notes:
Pisaster ochraceus feeds by everting their stomach and thus, digestion takes place outside of the body. They feed by grasping their prey and inserting their stomach into their victim to digest the prey's tissue. They can pull apart mussels using suction from their tube feet, which exerts as much as 4000 grams of sustained traction. However, they often don't need to, since their stomach can squeeze through a space as small as 0.1 mm. Thus, it can take advantage of a mussel's need to open its valves periodically to breathe or feed or even introduce its digestive enzymes through a narrow slit where the mussel's anchoring byssal threads pass between its valves. The diet of Pisaster ochraceus is influenced mostly by circumstance since where there are mussels, it eats mostly mussels and where mussels are absent, it east mostly barnacles, snails, limpets, and chitons.
 
April - June  
Reproduction:
Pisaster ochraceus has separate sexes and reproduces through broadcast spawning. This involves both sexes releasing large amounts of gametes into the water and relies on no parental care. This method relies on chance and often only a small portion of young will survive. An advantage of this method is the high dispersal of young. Pisaster ochraceus spawns during April and May in Monterey Bay and a month or so later in Puget Sound.

Pisaster ochraceus develops through several larval stages, including a brachiolaria larva stage during which it in no way resembles the sea star it will later grow into. During this stage it uses ciliated arms to sweep food into its mouth as it glides through the water column. Later, it attaches itself to the substratum, undergoes metamorphosis and grows into the adult form.
 
References:
Alden, P., F. Heath, R. Keen, A. Leventer, and W. Zomlefer. 2002. National Audubon Society Field Guide to California. A.A. Knopf, New York, NY.

Gotshall, D. 2005. Guide to marine invertebrates : Alaska to Baja California. Sea Challengers, Monterey, CA. 117 p.

Langstroth, L. and L. Langstroth. 2000. A Living Bay: The Underwater World of Monterey Bay. University of California Press, Berkeley and Los Angeles, CA. 287 p.

MARINe. 2004 (Updated 12/09/04). Multi-Agency Rocky Intertidal Network. World Wide Web electronic publication, http://www.marine.gov, Accessed [04/22/06]

Meinkoth, N.A. 1998. National Audubon Society Field Guide to North American Seashore Creatures. A.A. Knopf, New York, NY. 813 p.

Ramirez, Y. 2002. Pisaster ochraceus, Animal Diversity Web. World Wide Web electronic publication. Accessed July 26, 2006 at http://animaldiversity.ummz.umich.edu, Acessed [07/26/06].

Ricketts, E. F., J. Calvin, and J.W. Hedgpeth. 1985. Between Pacific tides. Stanford University Press, Stanford, CA. 652 p.

 
Data supplied by SIMoN Sanctuary Integrated Monitoring Network
Anthopleura xanthogrammica - Giant green anemone

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